Primitive Arthropods

The primitive arthropods, Onychophora (for example Peripatus) have a series of paired legs which are not jointed but have a ringed appearance because of the presence of rows of papillae on them. Each leg consists of two parts, a conical proximal part along with their extrinsic muscles, and a small distal part comprising a pair of claws.

Figure: Peripatus lateral view of head

The limbs are protracted and retracted. Using these legs, and through extension and contraction of the body for working the legs they crawl. While a segment is extended, the legs are lifted and moved forward; subsequent effective stroke provides the animals a pushing force.